Tomosynthesis of breast imaging procedures (DBT) has been investigated for several years as related to the possible use of this technology in screening for the early detection of breast cancer. Recently, a Food and Drug Administration (FDA) panel voted to strongly recommend approval for the clinical use of tomosynthesis in the United States. The fact is that, to date, all demonstrated possible benefits of tomosynthesis have been tested under conditions that apply to a small fraction of screened women, namely those without prior studies available for comparison, simulating the interpretation of baseline mammograms in the laboratory. The largest benefit demonstrated to date in this context is the possibility of substantially and significantly reducing recall rates, with some indications that observer performance in detecting specific mass like abnormalities could also be improved, albeit to a lesser extent. There are no data regarding the possible impact, if any, of tomosynthesis for women who have repeat screening mammograms; hence, a prior examination is available for comparison during the screening interpretation. This group constitutes the majority of screened women (60%-90% depending on the practice) and their recall rates are lower by approximately a factor of 1.5 to 2 as compared with baseline recall rates. As important, determining change (or no change) from prior observations (examinations) raises radiologists' confidence levels regarding their recommendations. DBT in combination with full field digital mammography (FFDM), which is the practice as presented for consideration before the recent FDA panel, requires approximately doubling the radiation dose. Before we unilaterally implement DBT in the screening environment, we need to assess the possible benefits of DBT when a prior examination is available during the interpretation. This is the very purpose of this study. To do so we propose to perform an observer performance study when prior FFDM examinations are available to the interpreter.